A: 

Hope I uderstood your question corectly.

You have multiple websites which are pointing to the same directory. You want to specify different default document for these websites.

In IIS7

Select the website -> Default Document 

Under "Actions" on the right hand side. Add the default document you want and remove the existing ones.

Shoban
Each website should have different Default Document. If i update one it applies to all other as it modifies web.config file.
eugeneK
Then I think est is to have an common default page (aspx) and then based on the URL redirect to a specific page.
Shoban
Sorry. Saw your answer after posting the above comment ;-)
Shoban
A: 

found the answer different default documents using rewrite map

eugeneK